Process for the preparation of nitro derivatives



United States Patent PROCESS FOR THE PREPARATION OF NITRO DERIVATIVESCharles Philip Spaeth, Woodbury, NJ., assignor to E. I. du Pont deNemours and Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application April 16, 1957 Serial No. 653,073

14 Claims. (Cl. 260--644) The present invention relates to a process forthe preparation of nitro derivatives of alkanes, cycloalkanes, andaryl-substituted alkanes. More particularly, the present inventionrelates to a process for the liquid-phase nitration of alkanes,cycloalkanes, and aryl-substituted alkanes by an alkyl or cycloalkylnitrite.

Nitro derivatives of such hydrocarbons are useful as solvents and aschemical intermediates, particularly as intermediates for valuableamines. Heretofore, the nitro derivatives were prepared generally byprocesses involving the use of nitric acid as the nitrating agent. Thisnitrating agent, however, has not been entirely satisfactory from aneconomical viewpoint. Not only does the corrosive action of the agentnecessitate the use of expensive chrome-steel or glass-lined storage andhandling equipment, but also in most nitrations by nitric acid, largeamounts of undesirable oxidation products are formed, thus decreasingthe yield of desired nitro compounds. In addition to the economicdisadvantages incurred by the use of nitric acid, the nitricacid-hydrocarbon system is a two-phase system, and vigorous agitationmust be used to bring about the required intimate contact of thereactants. Moreover, in the nitric acid processes of the prior art thesubstitution of the nitro group cannot be limited solely to the alkylside-chain of an aryl-substituted alkane; in these processes, the nitrosubstituent also is introduced on the aromatic ring, giving undesirableby-products and lower yields of the desired products.

Accordingly, an object of the present invention is to provide a simpleand economical process for the nitration of alkanes, cycloalkanes, andaryl-substituted alkanes. Another object of the present invention is toprovide a process whereby the hydrocarbons are nitrated in a homogeneoussystem and in intimate contact with the nitrating reagent. A furtherobject of the present invention is to provide a nitration processwhereby nitro substituents can be introduced readily into the alkylsidechain of aryl-substituted alkanes without attendant ring nitration.

I have found that the foregoing objects may be achieved when I react analkyl or cycloalkyl nitrite with an alkane, cycloalkane, oraryl-substituted alkane at a temperature within the range of 140 and 300C. and at a pressure of at least 125 p.s.i. ga.

ICC

In accordance with the process of the present invention, an alkyl orcycloalkyl nitrite is admixed with a molar excess of an alkane,cycloalkane, or aryl-substituted alkane, and the mixture is maintainedat a temperature within the range of and 300 C. and a pressure of atleast 125 p.s.i. ga., said hydrocarbon being maintained substantially inthe liquid phase. 7

The following examples serve to illustrate specific embodiments of themethod of carrying out the process of the present invention. However,they will be understood to be illustrative only and not as limiting theinvention in any manner.

EXAMPLE 1 Cyclohexane was introduced into a reactor which had previouslybeen flushed with nitrogen, the reactor was pressurized to 400 p.s.i.ga. with nitrogen, and the cyclohexane was heated to about C. Then, amixture of n-butyl nitrite and cyclohexane was pumped into the reactorover a period of about 8 minutes, during which time the temperature andpressure were maintained sub stantially at the initial levels. After theaddition of the mixture was complete, additional hydrocarbon was fedthrough the pump and feed lines over a period of about 2 minutes toclear the pump and lines of substantially all the nitrite-cyclohexanemixture. The mole ratio of total cyclohexane to n-butyl nitrite used inthis experiment was 21. The charge then was cooled to about 35 C. andthe reactor was vented. The product mixture was removed, washed withdilute sodium bicarbonate solution, dried, and analyzed. The analysisshowed that nitrocyclohexane in 32% yield and oxidation products in 5.6%,yield were obtained.

When this procedure was repeated with the exception that the reactiontemperature was maintained at 125 C., no nitration occurred.

EXAMPLE 2 The procedure of Example 1 was repeated with the exceptionthat the reaction temperature and pressure were maintained at C. and 125p.s.i. ga., respectively. The analysis of the product mixture showedthat nitrocyclohexane in 48% yield and oxidation products in 11% yieldwere obtained.

EXAMPLE 3 The procedure of Example 1 again was repeated with theexception that the reaction temperature and pressure were maintained atabout 205 C. and 550 p.s.i. ga., respectively. The product mixture wasshown by analysis tocontain nitrocyclohexane (41% yield) and oxidationproducts (10% yield).

EXAMPLE 4 In a series of experiments made in accordance with theafore-described procedure, various hydrocarbons were nitrated by meansof n-butyl nitrite. The reaction conditions and results are summarizedin the following table.

Table I Mole Ratio Reaction Yield of Experi- Hydrocarbon of Hydro Temp.'Iime N ltro Derivative N itro ment; carbon] 0.) (mln.) Derlv.

N itrlte (percent) n-Nonane 18 ca. 213 Mixt. of primary and sec- 38ondary mononitrononanes. n-Decane 9 ca. 205 12 Mixt. of primary and sec-35 ondary mononitrodecanes. Ethylbenzene 25 ca. 215 7l-Nltro-l-phenylethane.-. 37 Toluene ca. 222 10 Nitrophenylmethane 27Ohlorocyc1ohexane 11 ca. 205 5 l-Ohloro-2-nitrocycl0hexane 27 p-Xylene20 ca. 205 10 a-Nitro-p-xylene 29 Methylcyclohexane- 21 ca. 214 10l-Methyl-l-nitroeyclohexane. 32 Secondary mononitro de- 24 rivative.2,3Dimethylbutane" 14 ca. 212 8 2,3-Dimethy1-2-nitrobutane-. 25Prifliary mononltro derlv- 13 a ve. Oumene 17 ca. 216 92-Nitro-2-phenylpropane...- 38 Cyclohexane 26 ca. 210 25 Nitrocyclohexano 1 In experiments A-E and K, the reaction pressure wasmaintained at 410 p.s.1. ga.; in the other experiments the pressure wasmaintained at 400 p.s.i. ga.

EXAMPLE 5 In another series of experiments carried out according to theprocedure of Example 1, cyclohexane was nitrated by means of variousnitrites under the following reaction conditions: temperature, ZOO-210C.; pressure, 400 psi. ga.; and reaction time, 8-9 minutes. The resultsof these experiments are summarized in Table II.

As may be seen by reference to the foregoing examples, the nitrationprocess of the present invention proceeds smoothly and rapidly to givenitro compounds to the major product without ring nitration and withoutthe formation of appreciable quantities of undesired oxidation products.As has been illustrated, the nitration does not proceed at temperaturesbelow about 140 C. However, good results are obtained at temperatures offrom 140 C. up to about 300 C.; at higher temperatures, tar begins to beformed and yields are correspondingly decreased.

Pressure is applied to the reaction system in order to maintain thehydrocarbon substantially in the liquid phase. The exact pressureapplied, therefore, is dependent upon the temperature maintained in thereaction zone. Generally, the reactor will be pressurized to at least125 p.s.i. ga., a minimum pressure of 125 p.s.i, ga. usually beingrequired to maintain the liquid phase at the temperatures used in theprocess. The maximum pressure employed is governed only by themechanical limitations of the available equipment. However, because theuse of extremely high pressures, i.e. above 1000 atmospheres, does notresult in any advantages from the standpoint of yield, this figurerepresents the practical upper limit of pressure. The reactor can bepressurized with any inert gas, inasmuch as the specific inert gas usedis not critical. In addition to the nitrogen which was exemplified,carbon dioxide and helium also can be used.

In carrying out the nitration, a molar excess of the hydrocarbon isused, the unreacted hydrocarbon simply being recovered and reusedwithout deleterious effects upon the economics of the process. Moreratios of hydrocarbon-alkyl nitrite within the range of 5 to 44 havebeen exemplified and essentially equivalent results were obtained.Therefore, the extent of the excess of the bydrocarbon is not criticalto the process of the present invention, nor is the reaction time. Thereaction time was varied from 5 to 25 minutes without seriouslyeffecting the yield of nitro hydrocarbon. Since the re action proceedsso rapidly, good results are obtained in a matter of minutes andextensive reaction periods are not required.

Although the process has been exemplified by the use of cyclohexyl,n-butyl, isobutyl, and tert-butyl nitrites, any alkyl or cycloalkylnitrite is suitable for use as the nitrating agent, the nitrite group ofthe molecule being the portion of the molecule which eifects thenitration. Other suitable nitrating agents include ethyl nitrite,n-propyl and isopropyl nitrite, mixed amyl nitrites, hexyl nitrite, and.1,4-butyl dinitrite among others.

The process of the present invention is general for alkanes,cycloalkanes, and aryl-substituted alkanes which can be maintained inthe liquid phase under the reaction conditions. In addition to thehydrocarbons used in the experiments described in the forgoing examples,various other hydrocarbons can be nitrated by the process of the presentinvention. For example, additional nitro paraflins can be preparedreadily from the corresponding parafiinic hydrocarbons, e.g. n-hexane,neohexane, and isooctane. Other cycloalkanes which can be nitrated bythe present invention include, among others, cycloheptane andcyclopentane. The term cyeloalkane as used throughout the specificationand claims also includes, of course, alkylsubstituted cycloalkanes suchas the exemplified methylcyclohexane and others, e.g., alkylatedcycloheptanes and cyclopentanes. Additional aryl-substituted alkanes,suitable for use in the process of the present invention are, forexample, cymene, durene, and diisopropylbenzene. Furthermore,nonhydrocarbon substituents, such as nitro or halo groups, present onthe hydrocarbons to be nitrated do not interfere in the carrying out ofthe process of the present invention, and compounds such asnitrocyclohexane, chlorodecane, bromopentane, etc. constitute suitablestarting materials. Of course, when a nitro-substituted hydrocarbon isused as the starting material, a poly-nitro derivative is obtained whichcontains an additional nitro group.

Although the preceding examples illustrate the process as a batchwiseprocess, equally feasible is the carrying out of the process in acontinuous manner. For example, the alkyl or cycloalkyl nitrite and thehydrocarbon may be introduced continuously into a reaction zonemaintained at the desired operating conditions, while the productmixture is continuously withdrawn.

The invention has been described in detail in the foregoing. It will beapparent to those skilled in the art that many variations are possiblewithout departure from the scope of the invention. For example, thehydrocarbon to be nitrated may be admixed with a diluent, e.g. benzeneor acetonitrile, which is inert to the alkyl or cycloalkyl nitrite underthe reaction conditions. I intend therefore, to be limited only by thefollowing claims.

I claim:

1. A process for the preparation of nitro derivatives of alkane,cycloalkane, and simple mononuclear aryl-substituted alkane hydrocarbonswhich comprises admixing a nitrite selected from the group consisting ofthe lower alkyl nitrites and cycloalkyl nitrites with a molar excess ofsaid hydrocarbons in a reaction zone maintained at a temperature withinthe range of 140 and 300 C. and at a pressure of at least 125 p.s.i.ga., said hydrocarbons being maintained substantially in the liquidphase.

2. Process according to claim 1, wherein the nitrite is cyclohexylnitrite.

3. Process according to claim 1, wherein the nitrite is is a butylnitrite.

4. Process according to claim 1, wherein the reaction zone ispressurizedwith an inert gas selected from the group consisting ofnitrogen, helium, and carbon dioxide.

5. A process for the preparation of nitrocyclohexane which comprisesadmixing a nitrite selected from the group consisting of the lower alkylnitrites and cycloalkyl nitrites with a molar excess of cyclohexane in areaction zone maintained at a temperature within the range of 140 and300 C. and at a pressure of at least 125 p.s.i. ga., said cyclohexanebeing maintained substantially in the liquid phase.

6. Process for the preparation of nitro derivatives of n-decane whichcomprises admixing a nitrite selected from the group consisting of thelower alkyl nitrites and cycloalkyl nitrites with a molar excess ofn-decane in a reaction zone maintained at a temperature within the rangeof 140 and 300 C. and at a pressure of at least 125 p.s.i. ga., saidn-decane being maintained substantially in the liquid phase.

7. Process for the preparation of l-nitro-l-phenylethane which comprisesadmixing a nitrite selected from the group consisting of the lower alkylnitrites and cycloalkyl nitrites with a molar excess of ethylbenzene ina reaction zone maintained at a temperature within the range of 140 and300 C. and at a pressure of at least 125 p.s.i. ga., said ethylbenzenebeing maintained substantially in the liquid phase.

8. Process for the preparation of a-nitro-p-xylene which comprisesadmixing a nitrite selected from the group consisting of the lower alkylnitrites and cycloalkyl nitrites with a molar excess of p-xylene in areaction zone maintained at a temperature within the range of 140 and300 C. and at a pressure of at least 125 p.s.i. ga., said p-xylene beingmaintained substantially in the liquid phase.

9. Process for the preparation of nitrophenylmethane which comprisesadmixing a nitrite selected from the group consisting of the lower alkylnitrites and cyc1o alkyl nitrites with a molar excess of toluene in areaction zone maintained at a temperature within the range of 140 and300 C. and at a pressure of at least p.s.i. ga., said toluene beingmaintained substantially in the liquid phase.

10. Process for the preparation of l-chloro-Z-nitrocyclohexane whichcomprises admixing a nitrite selected from the group consisting of thelower alkyl nitrites and cycloalkyl nitrites with a molar excess ofchlorocyclohexane in a reaction zone maintained at a temperature withinthe range of and 300 C. and at a pressure of at least 125 p.s.i. ga.,said chlorocyclohexane being maintained substantially in the liquidphase.

11. Process for the preparation of nitro derivatives ofmethylcyclohexane which comprises admixing a nitrite selected from thegroup consisting of the lower alkyl nitrites and cycloalkyl nitriteswith a molar excess of methylcyclohexane in a reaction zone maintainedat a temperature within the range of 140 and 300 C. and at a pressure ofat least 125 p.s.i. ga., said methylcyclohexane being maintainedsubstantially in the liquid phase.

12. Process for the preparation of nitro derivatives of2,3-dimethylbutane which comprises admixing a nitrite selected from thegroup consisting of the lower alkyl nitrites and cycloalkyl nitriteswith a molar excess of 2,3-dimethylbutane in a reaction zone maintainedat a temperature within the range of 140 and 300 C. and at a pressure ofat least 125 p.s.i. ga., said 2,3-dimethylbutane being maintainedsubstantially in the liquid phase.

13. Process for the preparation of 2-nitro-2-phenylpropane whichcomprises admixing a nitrite selected from the group consisting of thelower alkyl nitrites and cycloalkyl nitrites with a molar excess ofcumene in a reaction zone maintained at a temperature within the rangeof 140 and 300 C. and at a pressure of at least 125 p.s.i. ga., saidcumene being maintained substantially in the liquid phase.

14. A process for the preparation of nitro derivatives of n-nonane whichcomprises admixing a nitrate selected from the group consisting of thelower alkyl nitrites and cycloalkyl nitrites with a molar excess ofn-nonane in a reaction zone maintained at a temperature within the rangeof 140 and 300 C. and at a pressure of at least 125 p.s.i. ga., saidn-nonane being maintained substantially in the liquid phase.

No references cited.

'3 I 8 'UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 4 PatentN00 2,883,433 April 21, 1959 Charles Philip Spaeth It is herebycertified thet error appearsjjin the printed specification of the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below, i 5

Column 3, line 42', for "compounds to" read compounds es line '72,

for "More" read Mol'e v--\-,

Signed and sealed this 13th day of October 1959.

,- (SEAL) KARL H. AXLINE Attest:

., ROBERT c. WATSO Ni Attesting'Officer Comnissioner of Patent 'UNITEDSTATES PATENT OFFICE v CERTIFICATE OF CORRECTION Pasnt "N5. 2,883,433April 21, 1959 Charla; Philip Spaeth It is'hreby certified @1151; errorappearin the printed specification of the above numbered. patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 42', for ompounds to" read compounds is line 12 fdf"More" rezad Mole" si ed and .sg zialeq this 13th d of October 1959 V(SEADI At fieet: v v r v H X I r ROBERT c. WATSONi Attesting; Officer(blm'lissioner of Patent UNITE-D STATES PATENT OFFICE CERTIFICATE OFCORRECTION Paini "Na. 2,883,433 April .21, 1959 Charles Philip spaeih Itjig hereby cert:uf'ied that error 'apparsjjin the printed specificationof the above numbred patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 3, line 42,- for' oompounds to" read compounds as fcir "More"read Mole" PM. I

si ned and; .sgaieq this 13th day of October 1959.

(SEAL) Atffiest:

' K RL X I Attesting; Officer ROBERT c. wATsori Cunniasioner of Patentsline 72

1. A PROCESS FOR THE PREPARATION OF NITRO DERIVATIVES OF ALKANE,CYCLOALKANE, AND SIMPLE MONONUCLEAR ARYL-SUBSTITUTED ALKANE HYDROCARBONSWHICH COMPRISES ADMIXING A NITRITE SELECTED FROM THE GROUP CONSISTING OFTHE LOWER ALKYL NITRITES AND CYCLOALKYL NITRITES WITH A MOLAR EXCESS OFSAID HYDROCARBONS IN A REACTION ZONE MAINTAINED AT A TEMPERATURE WITHINTHE RANGE OF 140 AND 300* C. AND AT A PRESSURE OF A LEAST 125 P.S.I.GA., SAID HYDROCARBONS BEING MAINTAINED SUBSTANTIALLY IN THE LIQUIDPHASE.